What might be styled the Soviet Union vs. Malcolm Toon or perhaps Malcolm Toon vs. the Soviet Union escalated yesterday when the Soviets publicly accused the American ambassador here of "slandering" the Soviet state and acting "extremely undiplomatically."

There have been previous skirmishes, both private and public, between the tart-tongued diplomat and the Russians. While these go back more than a decade, yesterday's commentary in the Communist Party daily Pravda was the sharpest attack on an American envoy in years

Why Pravda should choose this moment to rebuke Toon for a speech he made in Atlanta, Ga., is unclear to Western diplomatic sources here. To some, the article seems especially maladroitly timed, coming as it does just a week before Secretary of State Cyrus Vance arrives here for negotiations on a new strategic arms agreement - with Toon as one of his principal advisers.

To others, it is just one more sign of the especially high irritation the outspoken Toon causes the Soviet leadership, one more example, as if more were needed, that the Soviets will lose no chance to criticize the envoy. Expressing this view, one source said, "Maybe they are trying to show how little regard they have for amenities when it comes to dealing with Toon."

Yet another source suggested that the Soviets are deliberately trying to demonstrate that they hold Toon's advice to his secretary of state in little regard. [In Washington, the State Department issued the following statement: "The Department of State believes that the aspersions cast by Pravda on the conduct and ability of Ambassador Toon are unwarranted. The department does not believe that it is necessary to comment further on the Pravda allegations."]

Under a four-column, boldface headline "Is He Within His Role?" Pravada's commentary, most sources here believe, is a riposte cleared before publication by high officials of the Soviet Foreign Ministry.

Toon, 62, returns here today from several weeks of speaking engagements in the United States, a tour reportedly designed by the Carter administration to help enhance the motion of a new SALT agreement among conservatives. The Pravda commentary also touched on remarks Toon made in other cities before his Atlanta appearance.

Pravda said Toon "knit absurdities" in saying that the Soviet Union is a racist society, that he "again has told tales" for saying that the U.S. Embassy here is bombarded with microwave radiation, and that there is no explanation for the envoy's characterization of Soviet fears of China. In his Atlanta remarks, Toon said the Russians are "paranoid" about Peking.

"One thing is clear," the commentary summarized: "Diplomat Toon conducts himself extremely undiplomatically. What he is doing is not to the credit of this ambassadorship."

Citing the 1961 Vienna accord on diplomatic relations, Pravda asserted that Toon "forgets his task" of improving relations between his own country and the nation to which he is accredited.

"Neither in the convention nor in some other international documents is there even half a word that the diplomat is allowed to be busy publicly slandering the states whose hospitality he uses," Pravda said.

The commentary rebuked Toon also for remarks he apparently made about a month ago criticizing recent political trials and supression of human rights dissidents.

"The ambassador must be aware that in the Soviet Union, all forms of racisim, racial discrimination and implanting national discords have been denounced as illegal and are prosecuted in the strictest way," it said.

Said one source about the article: "Gratuitously offensive. It is one thing not to like what Toon says and to tell him so privately. This is quite another thing." The source speculated that there may have been other private expressions of dissatisfaction by the Kremlin over the bluntness of some of Toon's statements. "But they can't think this is a good way to get rid of him. This earns a person another year in office."

But the Soviets have repeatedly made their irritation with the ambassador crystal clear, and at the same time, managed to deal with him in a correct - if cold - fashion. Toon was denounced when he served here in the 1960s and the Kremlin delayed for three months accepting his appointment as ambassador in late 1976. He presented his credentials in January 1977.

It is a tenure that has been marked by unusual displays of official pique by the Soviets. Toon was barred from delivering a July 4 televsion speech last year because of official ire over human rights references in his remarks. But the next day, Toon was invited to the Kremlin for a personal talk with Soviet President Leonid Brezhnev.

In April, Toon was attacked in the weekly Literary Gazette for "activity hostile to Soviet society" for denouncing human rights repression here. Later that month, he participated in the most recent Vance visit here to discuss SALT.

Next week he will participate in the continuation of these talks.